This invention relates generally to vehicle guidance systems wherein a vehicle is guided for a portion of its flight in a command guidance mode and for another portion of its flight in a homing guidance mode. More particularly, the invention pertains to such vehicle guidance systems wherein a reference element having a known attitude orientation is required to be contained within such vehicle.
As is known in the art, a vehicle, such as a missible, may be guided towards a target by guidance signals developed from tracking data obtained either at a remote radar station or by radar means contained within the missile. The former system is commonly called a command guidance system and the latter a homing guidance system. For example, in a command guidance missile system wherein a missile is used to intercept an airborne target, a large, remotely located high resolution radar system and high speed digital computer may be provided for selecting one of a plurality of targets, tracking both the missile and the selected target, calculating proper guidance signals for the missile from generated tracking data, and transmitting such calculated guidance signals to the missile. As is known, a reference element such as an attitude stabilized platform, having an angular orientation which is known at the remote station, is generally required to be contained within such missile for enabling transformation of the transmitted guidance signals into missile control signals. Further, in a homing guidance missile system a smaller, light weight, low power tracking radar system may be provided for generation of both target tracking data and guidance signals. Such low power tracking radar system (or at least the receiver portion thereof as in a semi-active application) may, because of its relative lighter weight, be contained within the missile. Generally, such homing guidance system includes a target tracking antenna. Such target tracking antenna is generally gimballed to substantially eliminate the effect of missile body rate on the tracking data.
In one type of known missile systems, the features of command guidance and homing guidance techniques are combined. During the early portion of the missile's flight guidance signals are developed by a digital computer operated in response to signals obtained by tracking both the missile and a selected target with a high resolution radar system. During the latter portion of the flight guidance signals are obtained by tracking the target with the radar receiver portion of a radar system fed by a gimballed tracking element carried by the missile.
For reasons discussed above, such missile would require an attitude reference element during at least the early portion of the missile's flight. One arrangement considered for providing such an attitude stabilized reference is to use an attitude stabilized platform. Such an arrangement requires, additionally, a gimballed radar receiving antenna having at least two degrees of freedom with respect to the missile's body for providing tracking data during the latter portion of the missile's flight. The attitude stabilized platform generally includes: (a) three rate sensing gyros disposed to measure angular rates about a respective one of three mutually orthogonal axes; and (b), three corresponding drive means controlled, respectively, by each one of the rate sensing gyros to rotate, relative to the missile's body, the platform in a manner so as to compensate for any angular rotation experienced thereby. A common mechanism for providing such drive means is a mechanical servo. Such servos are relatively costly and are generally relatively heavy.